1. Technical Field
The present invention relates in general to the digital delivery systems. More specifically, the present invention relates to the delivery of multiformat digital video and digital audio data.
2. Background Art
Digital television offers viewers high-quality audio and video. For broadcasters, the compression of data provided by digital systems allow several programs to be delivered over the same analog bandwidth. Digital television can be distributed using adapted versions of current analog systems, including satellite, terrestrial, and cable. In all these systems, the audio and video components of a program are compressed at the source and multiplexed with other programs and system information needed to recreate the original program. The multiplexed signal is modulated and transmitted to the subscriber's home. A receiver at the subscriber's home demodulates the signal to recover the multiplexed digital streams, extracts the program of interest, and decodes the compressed audio and video for presentation on the television.
There are several variations of this system. For example, the digital stream can be modulated and broadcast over a coaxial cable system currently installed or delivered over satellite systems. In addition, the receiver may be a stand alone “set-top box” or may be integrated into directly into the television or other entertainment devices.
There are a variety of possible methods of encoding and delivering the digital television programs. To promote the development of interoperable components from different manufacturers, the Moving Picture Experts Group (“MPEG”) has created several different international standards. Of these, the MPEG-2 standard is particularly applicable to the delivery of digital television programs. This standard specifies the format of data as it is broadcast. The standard is composed of three primary parts covering systems, video and audio. The video and audio parts specify the format of the compressed video and audio data, while the systems part specifies the formats for multiplexing the audio and video data for one or more programs as well as information necessary for recovery of the programs. The MPEG-2 standard specifies two stream formats, one for error-free environments such as a digital storage mediums, and one for error-prone environments such as satellite, cable, ATM and other networks. The latter format, often referred to as the “transport stream” is used for broadcast applications. Turning to FIG. 5, a simplified block diagram of a MPEG-2 receiver is illustrated. A tuner extracts the analog signal, which is then digitized. The demodulator recovers the symbols, which represent the incoming bit stream. This group of functions is often referred to as the network interface-module (NIM). The final output of the NIM is the MPEG-2 transport stream, which is then fed into the transport demultiplexor.
The transport demultiplexor extracts the audio and video portions of the program to be sent to the audio and video decoders. The system data is delivered to system memory to enable the processor to process and act upon the information contained in the system data.
Current demultiplexors have limited capability of real-time filtering of the system data sent to system memory. As a result, all significant filtering must be done post-delivery to system memory via the processor and software. This software based filtering of system data can be computationally intensive, and significantly limits the ability of the system to process system data in real time.
Thus, what is needed is an improved transport demultiplexor that can filter data sent to memory to support further real time processing of the system data.